RESULTS OF PHASE-III EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY FOR MYOPIA

Objective: The purpose of the study is to determine safety and efficac y outcomes of excimer laser photorefractive keratectomy (PRK) for the treatment of mild-to-moderate myopia. Design: A prospective, multicent er, phase III clinical trial. Participants: A total of 701 eyes of 701 patients were entered in the study; 612 eyes were examined at 2 years after surgery. Intervention: Intervention was photorefractive keratec tomy using the Summit ExciMed UV200LA excimer laser (Summit Technology , Inc., Waltham, MA). The treatment zone diameter used was 4.5 mm in 2 51 eyes (35.8%) and 5 mm in 450 eyes (64.2%). Attempted corrections ra nged from 1.50 to 6.00 diopters (D). Main Outcome Measures: Predictabi lity and stability of refraction, uncorrected and spectacle-corrected visual acuity, refractive and keratometric astigmatism, corneal haze, contrast sensitivity, subjective reported problems of glare and halo, and patient satisfaction were the parameters measured. Results: At 2 y ears, 407 (66.5%) eyes achieved 20/20 or better uncorrected visual acu ity and 564 (92.5%) eyes achieved 20/40 or better visual acuity. Three hundred thirty-six (54.9%) eyes were within 0.5 D and 476 (77.8%) eye s were within 1.0 D of attempted correction. Stability of refraction i mproved with time; 86.8% of eyes were stable within 1.0 D from 6 to 12 months, 94% were stable from 12 to 18 months, and 96.3% were stable f rom 18 to 24 months. There was no evidence of progressive or late myop ic or hyperopic refractive shifts. One hundred fourteen (18.6%) eyes g ained 2 or more lines of spectacle-corrected visual acuity, whereas 42 (6.9%) eyes lost 2 or more lines; however, of the latter, 32 (76.2%) had spectacle-corrected visual acuity of 20/25 or better and 39 (92.9% ) eyes had 20/40 or better. Four hundred forty-two (72.2%) corneas wer e clear, 138 (22.5%) showed trace haze, 20 (3.3%) mild haze, 9 (1.5%) moderate haze, and 3 (0.5%) marked haze. On patient questionnaires, 87 (29.7%) patients reported worsening of glare from preoperative baseli ne; 133 (50.1%) reported worsening of halo symptoms from baseline. Con clusions: Photorefractive keratectomy appears effective for myopic cor rections of -1.50 to -6.00 D. Uncorrected visual acuity is maximized i n most eyes by 3 months, although some patients require between 6 mont hs and 1 year to attain their best postoperative uncorrected visual ac uity and some may require from 1 to 2 years for stabilization of refra ction. Refraction stabilizes progressively without evidence of late my opic or hyperopic refractive shifts. Optical sequelae of glare and hal o occur in some patients treated with a 4.5- or 5-mm treatment zone.